Some Egyptian guys called iPhoneIslam Team was able to hack iPad 3G and convert it to fully functional iPhone with Cydia tweak called PhoneItiPad that will arrive to Cydia soon.
With no special hardware, all you need is jailbroken iPad 3G and your iPad 3G will do anything you expect from iPhone … Phone Calls, SMS, FaceTime by phone number and more, thanks guys for the amazing job.
This tweak will be available via Cydia Store very soon. stay tuned